The long-term objective of this project is to leverage mobile technologies and crowdsourcing to create a new paradigm of evidence-based treatment delivery and dissemination, as current methods are often insufficient. The project seeks to refine and assess OC-Go, a HIPAA-compliant web-based clinician portal and patient-side mobile application designed to increase patient adherence to evidence-based treatment (EBT) for Obsessive Compulsive Disorder (OCD), a common and impairing condition, and provider ability to effectively implement EBTs. OC-Go allows clinicians to create and push tailored assignments to patients on their mobile devices with an optimized user interface that includes patient accountability and support features. Accordingly, patients can be guided to do assignments by themselves between sessions with increased fidelity over the course of treatment. OC-Go also directly empowers clinicians to learn from and teach one another via a searchable crowd-sourced (i.e., clinician-sourced) library of exposures, multimedia assignments, and assessments related to specific symptoms or search terms. Interactive assignments are created by clinicians or supervisors using a drop and drag toolkit and can include step-by-step written or audio instructions, patient video capture of exposures, writing assignments, speaking assignments, anxiety-cuing stimuli, exposure- oriented puzzles, cartoons, gaming templates, joint child-parent assignments, and many other types of creative technology-enabled activities. Once created and shared to the public library, any clinician can assign any task to any patient for homework or in-session use with one touch. The crowd-sourced library is rated by clinicians and curated for quality control. Use of OC-Go is expected to increase patient engagement, compliance, treatment efficiency, dissemination of EBTs, and therapist confidence and expertise. Phase I Specific Aims: Complete development of OC-Go: 1) Refine user interface via collaborative consultation and user acceptance testing (UAT) with community clinicians drawn from several treatment contexts and expert clinicians at a UCLA OCD specialty clinic; 2) Refine crowd-sourced library usability, expand search tools, and enable curating; 3) Assess strengths and weaknesses and refine key functions based on clinically- relevant outcomes and UAT in clinical piloting with OCD-diagnosed children (N=50 sessions/6 therapists). Phase II Specific Aims: Continued Development/Patient and clinician product testing: 1) Conduct randomized trial (N=32) to test compliance with therapeutic assignments (primary outcome), and treatment efficiency as defined by slope of clinical improvement over course of 6 sessions (secondary outcome) in EBT with and without OC-Go; 2) Simultaneously continue iterative improvements with UAT and seed the crowd- sourced library via partnership-sourcing with three prominent Child OCD clinics; 3) Then sequentially partner with community users in the field (N=100) to examine adoptability measures, product educational value, and to continue iterative product improvement given a large volume of users in ecologically valid settings.